Rubber composition comprising carbon black surface treated with silica

ABSTRACT

PCT No. PCT/JP96/03003 Sec. 371 Date Jun. 24, 1997 Sec. 102(e) Date Jun. 24, 1997 PCT Filed Oct. 16, 1996 PCT Pub. No. WO97/15620 PCT Pub. Date May 1, 1997A rubber composition containing at least one rubber component containing a diene rubber and a rubber reinforcing carbon black having silica deposited on the surface thereof.

TECHNICAL FIELD

The present invention relates to a rubber composition for tire usecontaining carbon black having silica deposited on the surface thereof(hereinafter referred to as "silica surface-treated carbon black"). Morespecifically, it relates to a rubber master batch composition containinga diene rubber and a surface-treated carbon black for rubberreinforcement having amorphous silica deposited on the surface thereof.Such a rubber composition containing silica surface-treated carbon blackmay be used for various types of rubber products such as cap treads,side treads, and belt cord covering rubber of tires, and other tirematerials and also belt conveyors, rubber rolls for industrial use,hoses, etc.

BACKGROUND ART

In the rubber industries, such as tire industry, carbon black forreinforcing the rubber is mixed with rubber in advance by a wet carbonblack master batch method whereby the process of kneading the carbonblack into the rubber has been attempted to be simplified andimprovements in the dispersibility of the carbon black in the rubberhave been attempted (for example, see Japanese Unexamined PatentPublication (Kokai) No. 59-49247 and Japanese Unexamined PatentPublication (Kokai) No. 63-43937).

Rubber compounds for tire use are usually used for applications whererepeated deformation is applied. If the tan δ of the rubber compound inthe high temperature region (for example, at 60° C.) is high, however,the amount of heat generated during use etc. becomes high, which isliable to lead to early breakage of the product such as tire. Thereforethere has been a need for lowering the tan δ in the high temperatureregion, while maintaining the grip on wet roads, the wear resistance,the breakage strength, and other performances. For example, in tirecompounds, improvement of the fuel consumption, durability, etc.requires that the tan δ be lowered in the high temperature region (40°C. to 100° C.), in particular at 60° C., but in general the brakingperformance (for example, wet grip), which is a contradictory property,falls as well. Thus, it becomes necessary to maintain this property.

In recent years, however, the appearance of superior silane couplingagents has led to the formulation of silica instead of carbon black.Silica has a lower tan δ at high temperatures (about 60° C.) comparedwith carbon black and a higher tan δ at low temperatures (about 0° C.),and therefore, when used for example for a rubber composition for a tiretread has the advantage of enabling production of a tire having a lowrolling resistance and a high grip.

As this prior art, for example, Japanese Unexamined Patent Publication(Kokai) No. 3-239737 proposes blending a silica filler with an SBRobtained by the solution polymerization method or a blend thereof and adiene rubber. Further, Japanese Unexamined Patent Publication (Kokai)No. 3-252431 proposes the blending of a silica filler and silanecoupling agent into an SBR obtained by the solution polymerizationmethod or a blend thereof with a diene rubber. Further, JapaneseUnexamined Patent Publication (Kokai) No. 3-253433 proposes the blendingof a silica filler and silane coupling agent with solutionpolymerization BR or SBR having silane modified terminals.

While, according to the above-mentioned proposals the tan δ at the hightemperature region can be reduced, without lowering the brakingperformance and other properties, however, the addition of the silicameans that the wear resistance is inferior to that when just addingcarbon black. Further, silica tends to make a high degree of selfagglomeration, and therefore, is not easy to disperse. Thus the problemof inferior processability is caused. Further, silica is nonconductive,therefore, when silica is used alone for tire use, in particular tiretread use, without the use of a sufficient amount (normally about 40parts by weight) of carbon black, results in insufficient flow of staticelectricity to the road surface and, as a result, charging and staticdischarge. The resultant discharge causes noise in the radio and otherelectronic apparatuses and in some cases causes erroneous operation ofthe same. Further, the vulcanization rate is slower, and therefore, avulcanization promoter becomes necessary and the cost becomes higher.

Covering the surface of the pigment etc. with silica etc. to improve thedispersibility and improve the weather resistance has been proposed, forexample, in Japanese Examined Patent Publication (Kokoku) No. 50-14254,Japanese Examined Patent Publication (Kokoku) No. 7-30269, etc. but noneof these alludes to the deposition of silica on the surface of thecarbon black for rubber reinforcement.

On the other hand, when blending silica with a rubber composition, it isdifficult to cause the dispersion of the silica during the kneading andtherefore a large amount of labor becomes necessary for the kneading.Thus, the preparation of master batches has been desired for silica likecarbon black. Silica, however, has a different agglomeration pH (about 4to 7) than the agglomeration pH region of carbon black (about 2.5 to 3),and therefore, in the past a satisfactory wet type silica master batchhas not been able to be obtained.

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide a rubbercomposition containing silica surface-treated carbon black which gives arubber composition having the superior tan δ temperature dependency ofsilica and an excellent wear resistance and also free from the problemsderived from a low electroconductivity.

Another object of the present invention is to provide a rubbercomposition for a tire which gives a rubber superior in wet grip androlling resistance compared with use of carbon black alone, superior inwear resistance and with a smaller electrical resistance compared withuse of silica alone, and therefore, free from the problem of noise inthe radio and other electronic apparatuses, and which is superior in thedispersibility as well.

A further object of the present invention is to provide a rubbercomposition which has a superior effect in lowering the rollingresistance and improving the cut resistance of rubber for use for sidetreads and improving the cord adhesion and improving the hardness ofrubber for use in covering belt cords.

In accordance with the present invention, there is provided a rubbercomposition comprising (a) at least one rubber component containing adiene rubber and (b) a rubber reinforcing carbon black having silicadeposited on the surface thereof.

In accordance with the present invention, there is also provided arubber composition comprising a rubber reinforcing surface-treatedcarbon black obtained by coagulating with a coagulating agent a mixtureof (a) 100 parts by weight, in terms of solid content, of rubber latexcontaining a diene rubber and (b) 10 to 250 parts by weight in terms ofsolid content, of a slurry of carbon black for rubber reinforcementhaving amorphous silica deposited on the surface thereof.

In accordance with the present invention, there is further provided arubber composition for tire use comprising at least one rubbercomponent-containing a diene rubber to which is blended surface-treatedcarbon black composed of rubber reinforcing carbon black having anitrogen specific surface area (N₂ SA) of 25 to 250 m² /g and a DBP oilabsorption of 70 to 180 ml/100 g on the surface of which is depositedwith 0.1 to 20% by weight of silica.

BEST MODE FOR CARRYING OUT THE INVENTION

The present inventors, as explained above, succeeded in obtaining arubber master batch composition containing silica by a wet methodproviding a rubber having the superior tan δ temperature dependency ofsilica, having an excellent wear resistance, and free from the problemsderived from a low electroconductivity by causing a completely novelrubber reinforcement surface-treated carbon black to coagulate with adiene rubber latex.

According to the present invention, as explained above, carbon blackhaving silica deposited (or precipitated) on the surface thereof (i.e.,silica surface-treated carbon black) is blended at least one rubberingredient containing a diene rubber. The amount of deposition of thesilica in the silica surface-treated carbon black is 0.1 to 20% byweight, preferably, 0.3 to 15% by weight. If the content of the silicais too small, the balance between the tan δ in the high temperatureregion (40° C. to 100° C.) and the tan δ in the low temperature region(about 0° C.) is liable not to be improved, while conversely if thecontent of the silica is too large, the electroconductivity will bedecreased, the agglomerating force of the filler will become stronger,and dispersibility during the kneading may become insufficient.

As the rubber reinforcement carbon black usable as the startingsubstance for manufacture of silica surface-treated carbon black for therubber reinforcement used in the present invention, any carbon blackgenerally used as carbon for reinforcement of rubber for tires etc. inthe past can be used. A preferable carbon black is a GPF to SAF grade ofrubber reinforcement carbon black produced by the oil furnace method.The type may be determined depending upon the application or utility ofthe rubber composition and blends of two or more types may be used aswell.

The silica surface-treated carbon black according to the presentinvention may be produced, for example, as follows. That is, the rubberreinforcing carbon black is first dispersed in water. To improve thedispersibility of the carbon black, a suitable dispersant, for example,methanol or various types of surfactants, is added to make a homogeneousslurry. Next, an amount of sodium silicate corresponding to the amountof silica to be deposited on the surface of the carbon black is added,under stirring, in the form of an aqueous solution, for example, to theaqueous slurry of carbon black thus obtained. Note that the amount ofsilica to be deposited on the surface of the carbon black is notparticularly limited, but is preferably 0.1 to 25% by weight based onthe weight of the silica surface-treated carbon black. If the amount ofdeposition of silica is too great, there is a tendency for difficulty incoagulation with the rubber latex. On the other hand, at the same timeas the aqueous solution of the sodium silicate, to neutralize the sodiumsilicate added, an acid, for example, sulfuric acid, hydrochloric acid,nitric acid, etc., is added with stirring. It is preferable to performthe addition of the aqueous solution of the acid and the addition of thesodium silicate simultaneously and in substantially the same amounts.The preferable feed rate of the sodium silicate is 0.001 to 0.110 g/min,in terms of the amount of silica, based upon 100 parts by weight ofcarbon black.

The pH of the reaction system at the stage of the abovesurface-treatment reaction is preferably 6 to 12, and the reactiontemperature is preferably from 50° to 95° C. from a practical viewpoint.In the stage of the above surface treatment reaction, after theamorphous silica is deposited on the surface of the carbon black, it ispossible to adjust the pH of the system to not more than 7, allow themixture to stand at a temperature of 50° to 95° C., with stirring, tocause aging and thereby obtain a slurry of the desired silicasurface-treated carbon black.

However, the silica surface-treated carbon black according to thepresent invention is not limited to this process of production. It mayalso be produced by placing carbon black produced by the oil furnacemethod etc. into an atmosphere for producing white carbon so as to causesilica to deposit on the surface of the carbon black.

The total amount of the silica in the rubber reinforcer produced by thismethod is not necessarily physically or chemically bonded to the surfaceof the carbon black, but observation by a transmission type electronmicroscope (about 600,000×) confirms that there is silica deposited onthe carbon black. Further, observation of the silica surface-treatedcarbon black obtained by kneading once with rubber, then pyrolyzing therubber ingredient in nitrogen also shows silica deposited on the carbonblack, and therefore, it is considered that the deposited silica andcarbon have bonds of a certain degree of strength.

The silica surface-treated carbon black according to the presentinvention has a nitrogen specific surface area (N₂ SA), measuredaccording to ASTM D 3037, of 20 to 250 m² /g, preferably 55 to 250 m² /gin the case of the rubber composition for a cap or under tread, 25 to120 m² /g in the case of the rubber composition for a side tread and 70to 150 m² /g, in the case of the rubber composition for a tire belt cordcovering. With a nitrogen specific area of less than 20 m² /g, thereinforcement of the rubber is insufficient and the breaking strengthand wear resistance may decrease, while conversely if the nitrogenspecific area is more than 250 m² /g, kneading into the rubber becomesdifficult and the dispersibility is liable to become poor.

The silica surface-treated carbon black according to the presentinvention has a DBP oil absorption, measured according to JIS K 6221, of70 to 180 ml/100 g, preferably 70 to 180 ml/100 g in the case of therubber composition for a cap or under tread, 70 to 150 ml/100 g in thecase of the rubber composition for a side tread, and 70 to 150 ml/100 gin the case of the rubber composition for a tire belt cord covering.

The rubber ingredient which is blended into the rubber compositionaccording to the present invention may be a rubber ingredient containinga diene rubber-alone or a mixture or two or more types. The blending ofthe silica surface-treated carbon black improves its wear resistance,grip performance, rolling resistance, etc.

As the diene rubber, any rubber which has been used for tires in thepast can be used. For example, natural rubber (NR), various types ofbutadiene rubbers (BR), various types of styrene-butadiene copolymerrubbers (SBR), polyisoprene rubber (IR), butyl rubber (IIR),acrylonitrile butadiene rubber, chloroprene rubber, styrene-isoprenecopolymer rubber, styrene-isoprene-butadiene copolymer rubber,isoprene-butadiene copolymer rubber, etc. may be mentioned. As otherrubbers, ethylene-propylene copolymer rubber, ethylene-propylene-dienecopolymer rubber, cblorosulfonated polyethylene, acryl rubber,epichlorohydrin, polysulfide rubber, silicone rubber, fluororubber,urethane rubber, etc. may be used. When mixtures of two or more typesare used, the ratio of the blend is not particularly limited.

According to the present invention, the silica surface-treated carbonblack is preferably added in 10 to 250 parts by weight, more preferably15 to 200 parts by weight, particularly preferably 10 to 100 parts byweight, to 100 parts by weight of the rubber ingredient. If the amountof formulation is too small, the desired effect cannot be obtained,while conversely if the amount is too large, the hardness becomes toohigh, the processability declines, and the practical value as a rubbermaterial may otherwise become unpreferably poor.

The rubber composition of the present invention may contain, in additionto the above-mentioned silica surface-treated carbon black, any carbonblack and/or silica usually blended into a rubber composition.

The amount of the ordinary carbon black and/or silica blended at thistime must be no more than 10 times the silica surface-treated carbonblack in weight, preferably no more than 8 times. If the amount of thecarbon black blended is too large, the desired effect cannot beobtained.

In preferable embodiments of the rubber composition of the presentinvention, there are provided rubber compositions for tire cap tread,under tread, side tread, and tire belt cord covering.

In the tire tread and under tread rubber compositions, the preferablerubber for inclusion as the rubber ingredient may be rubbers selectedfrom natural rubber (NR), polyisoprene rubber (IR), styrenebutadienecopolymer rubber (SBR), polybutadiene rubber (BR), butyl rubber (IIR),acrylonitrile butadiene rubber (NBR), etc.

As opposed to this, the rubber composition, for the tire side tread thepreferable rubber for inclusion as the rubber ingredient may be one ormore types of diene rubbers selected from NR, IR, BR, SBR, BR including1,2-syndiotactic polybutadiene, NR or BR including microfilaments (e.g.,nylon etc.) This is because the rubber for side tread requiresparticularly superior flex fatigue resistance and damage resistance.

In the rubber composition for tire belt cord covering, the rubberincluded as the rubber ingredient is preferably NR, IR, SBR, or BR. Thisis because toughness and bondability with steel cord or organic cord arerequired.

The rubber compositions according to the present invention for tire captread, under tread, side tread, and tire belt cord covering, asexplained above, include as fillers 10 to 200 parts by weight or 10 to100 parts by weight of a silica surface-treated carbon black based upon100 parts by weight of a rubber ingredient containing a diene rubber. Ifthe amount of the filler blended is too small, the tensile strength etc.of the rubber composition are decreased, while conversely if the amountis too large, the hardness and the heat generated along with deformationwill increase too much and exceed the practical range. In addition, theviscosity of the rubber composition when still unvulcanized will becometoo high. None of these is desirable.

In the present invention, the silica surface-treated carbon blackpreferably has a nitrogen specific surface area of 55 to 250 m² /g and aDBP oil absorption of 70 to 180 ml/100 g in the case of tire cap treadand under tread. If the value of the nitrogen specific surface area ofthe silica surface-treated carbon black is too low, the wear resistance,tensile strength, etc. are decreased, which are not desirable, while ifthe value is too high, the dispersibility at the time of kneading of therubber becomes difficult, which is also not desirable.

On the other hand, in the case of a rubber composition for a side tread,the silica surface-treated carbon black preferably has a nitrogenspecific surface area of 25 to 120 m² /g and a DBP oil absorption of 70to 150 ml/100 g. If this value is too low, the tensile strength,modulus, etc. again become low, while if the value is too high, in thenitrogen specific surface area, the heat generation becomes large, whichis again not desirable, and, in the DIBP oil absorption, when a DBP oilabsorption is less than 70 ml/100 g, the cut resistance is decreased,while when the DBP oil absorption is more than 150 ml/100 g, the crackresistance is decreased.

In the case of the rubber composition for a tire belt cord covering, thesilica surface-treated carbon black preferably has a nitrogen specificsurface area of 70 to 150 m² /g and a DBP oil absorption of 70 to 150ml/100 g. If this value is too low, the modulus becomes low, whileconversely if the value is too high, the viscosity of the unvulcanizedrubber at the time of rolling becomes high and the processing becomesdifficult.

The properties of the carbon black other than that surface treated withsilica, which is sometimes mixed into the rubber composition for tiretread, under tread, side tread and belt cord covering according to thepreferable embodiments of the present invention are not particularlylimited, but preferably the carbon is one which is usually used forrubber, that is, as a particle size grade, the FEF to SAF grades.

According to the preferable embodiment of the present invention, asilane coupling agent is further blended into the above-mentioned rubbercomposition. The amount of the silane coupling agent blended is notparticularly limited, but one of the features of silica surface-treatedcarbon black is that it displays an effect in smaller amounts than inthe case of use of a usual silica. For example, it is possible to blendthis in 0.1 to 8% based upon the weight of the silica surface-treatedcarbon black blended. Of course, it is also possible to blend in agreater amount.

If the amount of the silane coupling agent blended is too large, notonly is there no particular improvement in the physical properties, butalso it is not preferable that the costs is increased and the scorchtime is shortened, etc.

As the silane coupling agent which may be used in the preferableembodiment of the present invention, any silane coupling agent which hasbeen blended into conventional rubber compositions together with asilica filler may be blended. As such a silane coupling agent, forexample, vinyltrichlorosilane, vinyltrimethoxy-silane,vinyltriethoxysilane, vinyltris(β-methoxyethoxy) silane,β-(3,4-ethoxycyclohexyl)ethylktrimethoxysilane,γ-glycydoxypropyltrimethoxysilane,γ-glycydoxypropyl-methyldiethoxysilane,γ-glycydoxypropyltriethoxysilane,γ-methacryloxypropylmethyldimethoxysilane,γmethacryloxypropyltrimethoxysilane,γ-methacryloxy-propylmethyldiethoxysilane,γ-methacryloxypropyl-triethoxysilane, N-β(aminoethyl)γ-aminopropyl-methyldimethoxysilane, N-β(aminoethyl)γ-aminopropyl-trimethoxysilane, N-β(aminoethyl)γ-aminopropyl-triethoxysilane, γ-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, N-phenyl-γ-amino-propyltrimethoxysilane,γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane,bis-(3- triethoxysilyl!-propyl)-tetrasulfan, etc. may be mentioned.

The rubber composition of the present invention may suitably contain, inaddition to the above-mentioned rubber, carbon black having silicadeposited on the surface thereof, and optional silane coupling agent,any compounding agent which is normally used in the rubber industry, forexample, sulfur, an organic peroxide, a softening agent, an antioxidant,a vulcanization accelerator, a filler, a plasticizer, etc., ifnecessary, in the normally used range. Further, for the process ofproduction of the rubber composition of the present invention, thekneading method, vulcanization method, and the like normally used in therubber industry may be used.

Further, the rubber composition containing silica surface-treated carbonblack according to the present invention may be produced by the samemethod as the normal wet type carbon black master batch method. In theabove method, a slurry of carbon black having silica deposited on thesurface thereof is produced then this is mixed with a diene rubber latex(e.g., SBR latex), in a suitable ratio. Next, in accordance with theconventional method of production of a carbon black master batch,sulfuric acid or another acid is added to cause coagulation. Further, aconventional coagulation agent (for example, high molecular weightcoagulant, NaCl, etc.) may be used. Next, the coagulated rubbercomposition is separated from the aqueous phase and is cleared ofmoisture by, for example, drying with hot air so as to obtain thedesired rubber master batch composition. Note that in the above process,it is possible to added an antioxidant, process oil, silane couplingagent, or other additive if necessary.

The silica surface-treated carbon black used in the present invention,as explained above, is produced by causing amorphous silica to depositon the surface of carbon black by a reaction of sodium silicate,sulfuric acid, etc. in, for example, a carbon black slurry, andtherefore the surface-treated carbon black exists in a slurry state.Therefore, the rubber composition of the present invention can beproduced even if this slurry is directly mixed with the rubber latexThis enables the elimination of the labor in the kneading of the silicainto the rubber and also results in an excellent dispersibility of thesilica in the rubber. Further, the step of recovering thesurface-treated carbon black from the slurry and drying it iseliminated--which contributes further to the reduction of themanufacturing costs.

In a preferable embodiment of the present invention, when performing theabove wet type mixing, it is possible to blend 10 to 200 parts by weightof other ingredients generally used in formulations of rubber in thepast, such as aroma oil, paraffinic oil, naphthenic oil, and otherprocess oils and/or synthetic plasticizers, liquid rubber, and otherliquids, based upon 100 parts by weight of the diene family rubber.

EXAMPLES

The present invention will now be further illustrated by, but is by nomeans limited to, the following Examples.

Example I-1 to I-5 and Comparative Examples I-1 to I-3

Preparation of Silica Surface Treated Carbon Black

As the carbon black, the rubber reinforcement carbon black shown inTable I-1 was used. 200 g of a 10 wt % aqueous solution of a carbonblack dispersant (i.e., methanol) was well mixed into 100 g of carbonblack (CB), then 1.8 liters of water was added while stirring to obtaina homogeneous carbon black slurry. Next, since the desired amount of thesilica to be deposited on the surface of the carbon black was, here, 10wt %, the corresponding amount of sodium silicate, that is, 33.3 g, wasweighed and diluted with 0.2 liter of water.

The carbon black slurry obtained above was heated to 90° C. and adjustedto pH 9. To this slurry was dropwise added the aqueous solution ofsodium silicate obtained above at a rate of 0.060 g/min with sufficientstirring At the same time, the pH of the system was adjusted to 9 byadding a 2.0 wt % aqueous solution of sulfuric acid.

When the addition of the aqueous solution of sodium silicate wascompleted, the mixture was allowed to stand, while maintaining a pH 10and a temperature of 90° C., while stirring for about 30 minutes (aging)to obtain the desired slurry-like substance (solid content of 4.0 wt %)including the surface-treated carbon black.

Measurement of Silica Content of Surface Treated Carbon Black

A sample of the surface-treated carbon black was pyrolyzed in anelectric furnace at 600° C., then the ash was treated with hydrofluoricacid and the reduction in weight expressed as the silica content as apercentage of the weight of the original surface-treated carbon. Theresults are shown in Table I-1.

                                      TABLE I-1    __________________________________________________________________________             Ex. I-1                    Comp. Ex. I-1                           Comp. Ex. I-2                                  Comp. Ex. I-3    __________________________________________________________________________    Type of filler             Surface-treated                    Carbon black*.sup.2                           Silica Carbon black/silica             carbon black*.sup.1    Amount of filler             50     50     50     25/25    (phr)    e    Type of polymer             SBR1502                    SBR1502                           SBR1502                                  SBR1502    Coagulation state             Good*.sup.3                    Good*.sup.3                           Silica/rubber                                  Silica/rubber                           separate*.sup.4                                  separate*.sup.4    Amount of silica             3.27   0.0    --     --    (wt %)    __________________________________________________________________________     *.sup.1 Surface-treated carbon black: Carbon black of N339 (Seast KH: mad     by Tokai Carbon Co.) on whose surface amorphous silica is deposited to 10     wt %     *.sup.2 Carbon black N339 (Seast KH: made by Tokai Carbon Co.)     *.sup.3 Filler and rubber integral. Filler homogeneously dispersed in     rubber.     *.sup.4 Filler and rubber are separately present. A part of filler in the     rubber does not homogeneously disperse in the rubber.

                    Ex. I-3 Ex. I-4                                   Ex. I-5    __________________________________________________________________________    Type of filler             Surface-treated                    Surface-treated                            Surface-treated                                   Surface-treated             carbon black*.sup.1                    carbon black*.sup.2                            carbon black*.sup.3                                   carbon black*.sup.4    Amount of filler             50     50      50     50    (phr)    Type of polymer             SBR1502                    SBR1502 5BR1502                                   SBR1502    Coagulation state             Good*.sup.5                    Good*.sup.5                            Good*.sup.5                                   Good*.sup.5    Amount of silica             3.27   3.32    3.22   3.35    (wt %)    __________________________________________________________________________     *.sup.1 Surface-treated carbon black: carbon black of GPF (Seast V: made     by Tokai Carbon Co.) on surface of which amorphous silica is deposited to     10 wt %.     *.sup.2 Surfacetreated carbon black: carbon black of FEF (Seast SO: made     by Tokai Carbon Co.) on surface of which amorphous silica is deposited to     10 wt %.     *.sup.3 Surfacetreated carbon black: carbon black of ISAF (Seast 6: made     by Tokai Carbon Co.) on surface of which amorphous silica is deposited to     10 wt %.     *.sup.4 Surfacetreated carbon black: carbon black of SAF (Seast 9: made b     Tokai Carbon Co.) on surface of which amorphous silica is deposited to 10     wt %.     *.sup.5 Filler and rubber are integrated. Filler homogeneously dispersed     in rubber.

Preparation of Rubber Composition Containing Surface-Treated CarbonBlack

Next, the surface-treated carbon black obtained above was made into aslurry (concentration of 12.5 wt %). 200 g of this slurry and 125 g ofSBR1502 latex (concentration of 41 wt %) were mixed. 1000 g of salinewater (concentration of 3 wt %) was added to this as a coagulant, thenthe mixture was stirred at a temperature of 50° C. for 0.5 hour toobtain the rubber reinforcing rubber composition containing silicasurface-treated carbon black.

Methods of Measurement of Physical Properties of Rubber

The physical properties of rubber were evaluated for a rubbercomposition of the present invention, that is, Example I-1 of Table I-1,in comparison with a case of kneading by the usual dry blend method anda case of use of carbon black.

Various types of rubber compositions were prepared by ordinary methodsby kneading the following formulations by a Bambury mixer and rollmachine (vulcanization conditions: 160° C.×30 minutes). The results areshown in Table I-2.

    ______________________________________    Formulation Table    ______________________________________    Diene rubber (SBR1502)                      100      parts by weight    Reinforcing filler (see Table I-1)                      50       parts by weight    Silane coupling agent*.sup.1                      3        parts by weight*.sup.2    Zinc oxide (JIS NO. 3)                      3        parts by weight    Stearic acid      2        parts by weight    Antioxidant*.sup.3                      2        parts by weight    Powdered sulfur   2        parts by weight    Vulcanization accelerator*.sup.4                      1        part by weight    ______________________________________     *.sup.1)Si 69 (made by Degussa Co.)     *.sup.2)Not used when reinforcing filler is carbon black     *.sup.3)Santoflex 13 (Made by Monsanto Corp.)     *.sup.4)Santocure NS (Made by Monsanto Corp.)

                                      TABLE I-2    __________________________________________________________________________               Ex. I-6     Comp. Ex. I-4                                       Comp. Ex. I-5    __________________________________________________________________________    Master batch used               Ex. I-1 composition                           None, dry blend                                       None, dry blend    Type of reinforcing filler               Surface-treated                           Carbon black*.sup.2                                       Silica*.sup.3               carbon black*.sup.1    Kneading time*.sup.4               1 min.                     4 min.                           2 min.                                 4 min.                                       2 min.                                             4 min.    Kneading state*.sup.4               No problem                     No problem                           Carbon                                 No problem                                       Carbon                                             No problem                           intake poor intake poor    tan δ 60° C.*.sup.5               0.158 0.160 --    0.186 --    0.159    tan δ 0° C.*.sup.5               0.310 0.307 --    0.305 --    0.310    Wear resistance index*.sup.6               99    101   --    100   --    76    __________________________________________________________________________     *.sup.1 Surface-treated carbon black: carbon black of N339 (Seast KH: mad     by Tokai Carbon Co.) on whose surface amorphous silica is deposited to 10     wt %.     *.sup.2 N339 Seast KH (made by Tokai Carbon)     *.sup.3 Nipsil AQ (made by Nippon Silica Kogyo Co.)     *.sup.4 Performed by 1.5 liter Banbury mixer. Rubber and compounding     agents (excluding vulcanization system) simultaneously added. State after     being discharged a predetermined time later is observed.     *.sup.5 Viscoelasticity spectrometer made by Toyo Seiki Seisakusho used     and tan δ measured under conditions of temperature of 0° C.     or 60° C., static stress of 10%, dynamic stress of ± 2%, and     frequency of 20 Hz.     *.sup.6 Lambourn wear tester used for measurement under conditions of roo     temperature, slip ratio of 35%, and load of 6 kg. Results expressed as     index using one carbon black formulation as 100. The larger the figure,     the better the wear resistance shown.

Example II-1 to II-14 and Comparative Example II-1 to II-19

Preparation of Silica Surface-Treated Carbon Black

The silica surface-treated carbon black was prepared by the followingmethod. That is, carbon black slurry was prepared according to anordinary method and warmed to 90° C., then diluted JIS No. 1 sodiumsilicate was added by a constant feed pump, while maintaining a pH of 5to 10 with dilute sulfuric acid and an aqueous solution of sodiumhydroxide so as to cause silica to deposit on the carbon surface. Next,the pH was made 6 and the mixture was allowed to stand for 1 hour, thenwas filtered, washed with water, and dried to obtain the desiredsubstance. The change of the silica content was performed by adjustingthe amount of addition of the sodium silicate and the pH of the system.

The silica content in the silica surface-treated carbon black (CB) wasfound by pyrolyzing the silica surface-treated carbon black in anelectric furnace at 600° C., then performing fluorination and thefollowing processing and then finding the content by the followingformula:

    Silica content (%)= Loss of weight due to fluorination/Weight of surface-treated carbon black!×100

Fluorination: About 200 mg of the sample was weighed with and placed ina polyethylene beaker. This was moistened with distilled water, then 5mg of hydrofluoric acid was added. This was stirred and allowed to standfor 5 minutes, then was suction filtered, washed well with water, anddried.

The properties of the prepared silica surface-treated carbon black areshown in Table II-1. The methods of measurement are as explained below.

Nitrogen specific surface area: ASTM D3037

DBP oil absorption: JIS K6221 "Test Methods for Carbon Black for

                                      TABLE II-1    __________________________________________________________________________    (Properties of Surface-Treated Carbon Black)                 Original carbon black properties                       Nitrogen specific                 Carbon black                       surface area                               DBP oil absorption                                        Silica                 grade m.sup.2 /g                               ml/100 g wt %    __________________________________________________________________________    Surface-treated carbon black 1                 HAF (N339)                        94     132       0.6    Surface-treated carbon black 2                 "     "       "         5.5    Surface-treated carbon black 3                 "     "       "        10.8    Surface-treated carbon black 4                 "     "       "        18.3    Surface-treated carbon black 5                 "     "       "        25.0    Surface-treated carbon black 6                 ISAF (N220)                       111     115      10.1    Surface-treated carbon black 7                 ISAF-HS                       125     170      10.7    Surface-treated carbon black 8                 SAF (N110)                       144     118      10.2    __________________________________________________________________________

The basic formulations (parts by weight) of the various rubbercompositions used in the following Examples and Comparative Examples areshown in Table II-2 (Formulation 1), Table II-3 (Formulation 2), andTable II-4 (Formulation 3).

                  TABLE II-2    ______________________________________    SBR1502*.sup.1  100    Reinforcing filler                    Carbon black, silica surface-                    treated carbon suitably used    Silane coupling agent*.sup.2                    q.s.    Vulcanization promoter*.sup.3                    q.s.    Zinc white      3    Stearic acid    2    Antioxidant*.sup.4                    2    Wax             1    Sulfur          1.8    Vulcanization accelerator*.sup.5                    0.8    ______________________________________     *.sup.1)NIPOL 1502: made by Nippon Zeon Co.     *.sup.2)Si 69: made by Degussa Co.     *.sup.3)Diethylene glycol     *.sup.4)Santoflex 13: made by Monsanto Corp.     *.sup.5)Santocure NS: made by Monsanto Corp.

                  TABLE II-3    ______________________________________    Solution polymerization SBR*.sup.1                      35    Natural rubber    65    Reinforcing filler                      Carbon black, silica, surface-                      treated carbon suitably used    Silane coupling agent*.sup.2                      q.s.    Vulcanization promoter*.sup.3                      q.s.    Zinc white        3    Stearic acid      2    Antioxidant*.sup.4                      2    Wax               1    Sulfur 2    Vulcanization accelerator*.sup.5                      1    ______________________________________     *.sup.1)NIPOL NS 116: made by Nippon Zeon Co.     *.sup.2)Si 69: made by Degussa Co.     *.sup.3)Diethylene glycol     *.sup.4)Santoflex 13: made by Monsanto Corp.     *.sup.5)Santocure NS: made by Monsanto Corp.

                  TABLE II-4    ______________________________________    Solution polymerization SBR*.sup.1                      65    BR*.sup.2         35    Reinforcing filler                      Carbon black, silica, surface-                      treated carbon suitably used    Silane coupling agent*.sup.3                      q.s.    Vulcanization promoter*.sup.4                      q.s.    Zinc white        3    Stearic acid      2    Antioxidant*.sup.5                      3    Wax               1.5    Aroma oil         30    Sulfur            1.7    Vulcanization accelerator*.sup.6                      0.8    ______________________________________     *.sup.1)NS 116: made by Nippon Zeon Co.     *.sup.2)NIPOL BR 1220: made by Nippon Zeon Co.     *.sup.3)Si 69: made by Degussa Co.     *.sup.4)Diethylene glycol     *.sup.5)Santoflex 13: made by Monsanto Corp.     *.sup.6)Santocure NS: Made by Monsanto Corp.

Various rubber compositions were prepared by the formulations of TableII-5 (Examples II-1 to II-8 and Comparative Examples II-1 to II-9),Table II-6 (Examples II-9 to II-10 and Comparative Examples II-10 to13), Table II-7 (Example II-11 to II-12 and Comparative Examples II-14to II-17), and Table II-8 (Examples II-13 to II-14 and ComparativeExamples II-18 to II-19) (using the above Formulation 1) (parts byweight) by an ordinary method by mixing and kneading by a Bambury mixerand kneading roller. These rubber compositions were vulcanized bypressing at 160° C. for 20 minutes to prepare the target test pieceswhich were then subjected to various types of tests to measure theirphysical properties. The results are shown in Table II-5 to Table II-8.Note that the test methods were as follows:

                                      TABLE II-5    __________________________________________________________________________               Comp.                   Comp.   Comp.                               Comp.                                   Comp.                                       Comp.               Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex.               II-1                   II-2                       II-1                           II-3                               II-4                                   II-5                                       II-6                                           II-2                                               II-3    __________________________________________________________________________    Carbon black N 339*.sup.1               40  --  --  50  --  --  --  --  --    Silica*.sup.2               --  40  --  --  50  50  50  --  --    Surface-treated               --  --  40  --  --  --  --  50  --    carbon 1*.sup.3    Surface-treated               --  --  --  --  --  --  --  --  50    carbon 2*.sup.3    Surface-treated               --  --  --  --  --  --  --  --  --    carbon 3*.sup.3    Surface-treated               --  --  --  --  --  --  --  --  --    carbon 4*.sup.3    Surface-treated               --  --  --  --  --  --  --  --  --    carbon 5*.sup.3    Silane coupling agent               --  4   2   --  5   2.5 5   2.5 2.5    Vulcanization promotor               --  2   --  --  2.5 2.5 --  --  --    Water resistance index               100 65  95  114 88  85  86  104 108    Wet braking performance               100 103 99  118 119 112 113 115 115    Rolling resistance index               100 93  87  121 106 109 108 105 109    Electrical resistance               1.1E                   1.8E                       3.2E                           1.2E                               1.5E                                   1.5E                                       2.0E                                           1.7E                                               3.6E    (Ω cm)               +3  +14 +14 +2  +14 +14 +14 +2  +2    Vulcanization               100 119 101 96  130 128 137 112 112    acceleration index    __________________________________________________________________________                        Comp.    Comp.                                      Comp.               Ex.  Ex. Ex.  Ex. Ex.  Ex. Ex.  Ex.               II-4 II-5                        II-7 II-6                                 II-8 II-9                                          II-7 II-8    __________________________________________________________________________    Carbon black N 339*.sup.1               --   --  --   20  60   --  --   --    Silica*.sup.2               --   --  --   --  --   60  --   --    Surface-treated               --   --  --   30  --   --  60   60    carbon 1*.sup.3    Surface-treated               --   --  --   --  --   --  --   --    carbon 2*.sup.3    Surface-treated               50   --  --   --  --   --  --   --    carbon 3*.sup.3    Surface-treated               --   50  --   --  --   --  --   --    carbon 4*.sup.3    Surface-treated               --   --  50   --  --   --  --   --    Silane coupling agent               2.5  2.5 2.5  1.5 --   6   3    3    Vulcanization promoter               --   --  --   --  --   3   --   2    Wear resistance index               109  104 103  107 128  110 114  114    Wet braking performance               116  117 117  117 135  136 132  133    Rolling resistance index               113  109 108  114 143  118 121  120    Electrical resistance               6.0E 9.7E                        1.1E 1.3E                                 4.5E 2.4E                                          7.6E 7.6E    (Ω cm)               +2   +3  +4   +2  +1   +14 +0   +0    Vulcanization               116  118 123  105 92   142 104  94    acceleration index    __________________________________________________________________________     *.sup.1 Carbon black N 339: Seast KH (made by Tokai Carbon Co.)     *.sup.2 Silica: Nipsil AQ (made by Nippon Silica Kogyo Co.)     *.sup.3 Surfacetreated carbon 1: see Table II1

                                      TABLE II-6    __________________________________________________________________________                Comp. Ex.                     Comp. Ex.                          Ex.  Comp. Ex.                                    Comp. Ex.                                         Ex.                II-10                     II-11                          II-9 II-12                                    II-13                                         II-10    __________________________________________________________________________    Carbon black N 220*.sup.1                 40  --   --    60  --   --    Silica*.sup.2                --   40   --   --   60   --    Surface-treated                --   --   40   --   --    60    carbon 6*.sup.3    Silane coupling agent                --    4    2         6    3    Vulcanization promoter                --    2   --   --    3   --    Wear resistance index                100  62   101  128  105  138    Wet braking performance                100  90   98   128  119  123    Rolling resistance                100  83   88   140  105  112    index    Electrical resistance                7.1E + 0                     1.8E + 14                          1.5E + 1                               6.7E - 1                                    2.4E + 14                                         1.1E + 0    (Ω cm)    Vulcanization acceleration                100  107  103   90  114  1oo    index    __________________________________________________________________________     *.sup.1 Carbon black N 220: Seast: 6 (made by Tokai Carbon Co.)     *.sup.2 Silica : Nipsil AQ (made by Nippon Silica Kogyo Co.)     *.sup.3 Surfacetreated carbon 6: see Table II1.

                                      TABLE II-7    __________________________________________________________________________                Comp. Ex.                     Comp. Ex.                          Ex.  Comp. Ex.                                    Comp. Ex.                                         Ex.                II-14                     II-15                          II-11                               II-16                                    II-17                                         II-12    __________________________________________________________________________    Carbon black ISAF-HS*.sup.1                 40  --   --    60  --   --    Silica*.sup.2                --   40   --   --    60  --    Surface-treated                --   --   40   --   --    60    carbon 7*.sup.3    Silane coupling agent                --    4    2   --    6    3    Vulcanization promoter                --    2   --   --    3   --    Wear resistance index                100  53   109  107   90  117    Wet braking performance                100  94   99   121  124  123    Rolling resistance                100  87   95   137  110  119    index    Electrical resistance                2.2E + 1                     1.8E + 14                          4.8E + 1                               5.0E + 0                                    1.5E + 14                                         8.0E + 0    (Ω cm)    Vulcanization acceleration                100  122  116   95  130  119    index    __________________________________________________________________________     *.sup.1 Carbon black ISAFHS: CD2005 (made by Colombian Chemicals Co.)     *.sup.2 Silica: Nipsil AQ (made by Nippon Silica Industry Co.)     *.sup.3 Surfacetreated carbon 7: see Table II1

                  TABLE II-8    ______________________________________               Comp Ex.                      Ex.      Comp. Ex.                                        Ex.               II-18  II-13    II-19    II-14    ______________________________________    Carbon black N 110*.sup.1                  60      --        80    --    Surface-treated                 --        60      --      80    carbon 8*.sup.2    Silane coupling agent                 --        3       --      4    Aroma oil     20       20       30     30    Wear resistance index                 100      107      112    117    Wet braking performance                 100      100      122    121    Rolling resistance                 100       93      129    116    index    Electrical resistance                 5.0 E + 0                          5.7 E + 0                                   8.7 E + 1                                          9.4 E - 1    (Ωcm)    Vulcanization acceler-                 100      108       98    110    ation index    ______________________________________     *.sup.1)Carbon black N 110: Seast 9 (made by Tokai Carbon Co.)     *.sup.2)Surfacetreated carbon 8: see Table II1

Methods of Measurement of Various Types of Physical Properties

Vulcanization Acceleration Index

A sample of unvulcanized rubber was tested by a rheometer at 160° C. tofind the T95. The result was shown as an index using one of the carbonblack formulations as 100. The smaller the figure, the less a delay invulcanization shown.

Wear Resistance

A Lambourn wear tester was used to measure the wear resistance underconditions of a room temperature, a slip ratio of 35%, and a load of 5kg. The result was shown as an index using one of the carbon blackformulations as 100. The larger the figure, the better the wearresistance.

Wet Braking Performance

A viscoelasticity spectrometer made by Toyo Seiki Seisakusho Co. wasused and the tan δ measured under conditions of a temperature of 0° C.,a static stress of 10%, a dynamic stress of ±2%, and a frequency of 20Hz. The results are shown as an index using one of the carbon blackformulations as 100. The larger the figure, the better the wet brakingperformance shown.

Rolling Resistance Index

A viscoelasticity spectrometer made by Toyo Seiki Seisakusho Co. wasused and the tan δ was measured under conditions of a temperature of 60°C., a static stress of 10%, a dynamic stress of ±2%, and a frequency of20 Hz. The results are shown as an index using one of the carbon blackformulations as 100. The smaller the figure, the smaller the rollingresistance.

Electrical Resistance

The volume specific resistance was measured by ASTM D991 or JIS K6911.

As clear from the results of Table II-5 to Table II-8, compared with therubber compositions of Comparative Examples II-1 to II-19 where ordinarycarbon black or silica was blended rather than blending thesurface-treated carbon black, the rubber compositions of Examples II-1to II-14 where surface-treated carbon black was blended gave rubber withan excellent wet braking performance and low rolling resistance whilemaintaining an excellent wear resistance. Further, with the examples ofthe invention, it was possible to reduce the electrical resistancecompared with formulations of silica.

Examples II-15 to II-16 and Comparative Examples II-20 to II-22

Various rubber compositions were prepared by the formulations (parts byweight) shown in the above Table II-3 and Table II-9 by an ordinarymethod by mixing and kneading by a Bambury mixer and kneading roller.These rubber compositions were vulcanized by pressing at 160° C. for 20minutes to prepare test pieces which were then subjected to varioustests. The results are shown in Table II-9. Note that the characteristicvalue of the reinforcing agent is a value including carbon black andsilica.

                                      TABLE II-9    __________________________________________________________________________                 Comp. Ex.                      Comp. Ex.                           Ex.  Ex.  Comp. Ex.                 II-20                      II-21                           II-15                                II-16                                     II-22    __________________________________________________________________________    Carbon black N 339*.sup.1                  50  --   --   --   --    Silica*.sup.2                 --   50   --   --   --    Surface-treated carbon 1*.sup.3                 --   --   50   --   --    Surface-treated carbon 2*.sup.3                 --   --   --   50   --    Surface-treated carbon 5*.sup.3                 --   --   --   --   50    Silane coupling agent                 --    4    2    2    2    Vulcanization promoter                 --    2   --   --    Wear resistance index                 100  75   99   98   97    Wet braking performance                 100  107  100  99   101    Rolling resistance index                 100  71   73   72   71    Electrical resistance                 1.23E + 2                      1.7E + 14                           2.0E + 2                                2.2E + 2                                     2.4E + 2    (Ω cm)    Vulcanization acceleration                 100  135  110  112  112    index    __________________________________________________________________________     *.sup.1 Carbon black N 339: Seast KH (made by Tokai Carbon Co.)     *.sup.2 Silica: Nipsil AQ (made by Nippon Silica Industry Co.)     *.sup.3 Surfacetreated carbon 1, 2, 5: see Table II1

As is clear from the results of Table II-9, when the silicasurface-treated carbon black of the present invention is blended insteadof the usual carbon black (Examples II-15 to II-16), as compared withthe case where just carbon black is blended (Comparative Example II-20)and the case where just silica is blended (Comparative Example II-21),the rolling resistance index is vastly improved, without detracting fromthe other properties.

Note that in the case where silica was used, (Comparative ExampleII-21), the rolling resistance was improved, but the wear resistancebecame poor and, further, as expected, the vulcanization rate becameslower.

Accordingly, the Examples of the present invention can be said toimprove the important properties of the wear resistance, wet brakingperformance, rolling resistance index, electrical resistance,vulcanization rate, etc. with a good balance.

Example II-17 and Comparative Examples II-23 to II-24

Various rubber compositions were prepared by the formulations (parts byweight) shown in Table II-4 and Table II-10 by an ordinary method bymixing and kneading by a Bambury mixer and kneading roller. These rubbercompositions were vulcanized by pressing at 160° C. for 20 minutes toprepare test pieces for cap treads which were then subjected to varioustests. The results are shown in Table II-10.

                  TABLE II-10    ______________________________________                 Comp. Ex.                         Comp. Ex. Ex.                 II-23   II-24     II-17    ______________________________________    Carbon black N 220*.sup.1                    80       --        --    Silica*.sup.2  --        80        --    Surface-treated                   --        --         80    carbon 6*.sup.3    Silane coupling agent                   --         8         4    Vulcanization promoter                   --         4        --    Wear resistance index                   100       79        103    Wet braking performance                   100       103       104    Rolling resistance index                   100       71         76    Electrical resistance (Ωcm)                   8.1 E - 1 2.1 E + 14                                       1.1 E + 0    Vulcanization acceler-                   100       131       110    ation index    ______________________________________     *.sup.1)Carbon black N 220: Seast 6 (made by Tokai Carbon Co.)     *.sup.2)Silica: Nipsil AQ (made by Nippon Silica Kogyo Co.)     *.sup.3)Surfacetreated carbon 6: see Table II1

As is clear from the results of Table II-10, by blending in thesurface-treated carbon black of the present invention, it is possible toobtain a rubber composition having an improved wear resistance and wetbraking performance and having a low electrical resistance and anextremely low rolling resistance.

INDUSTRIAL APPLICABILITY

As is clear from the results of Table I-1 and Table I-2, the rubbercomposition containing silica surface-treated carbon black according tothe present invention can be produced by a method the same as with anordinary carbon master batch. The resultant composition also gives arubber having a lower tan δ at a high temperature region (60° C.)compared with one with regular carbon black and does not fall in wearresistance. According to the present invention, further, by blending thesilica surface-treated carbon black, it is possible to give a rubberwhich is superior to one with regular carbon black and has a wet gripand low rolling resistance equal to or better than one with just silica.Further, compared with a conventional silica filler, the resultantelectrical resistance is small, and therefore, there is no problem ofgeneration of noise in the ratio or other electronic devices. Also, thedispersibility in a compound is good. In addition, the wear resistanceis superior than with silica alone and the vulcanization rate is notslow, and therefore, addition of a vulcanization accelerator etc. is notrequired.

We claim:
 1. A rubber composition comprising (a) at least one rubbercomponent containing a diene rubber and (b) a rubber reinforcing carbonblack having silica deposited on the surface thereof.
 2. A rubbercomposition as claimed in claim 1, wherein said composition is obtainedby coagulating with a coagulating agent a mixture of(a) 100 parts byweight, in terms of solid content, of rubber latex containing a dienerubber and (b) 10 to 250 parts by weight, in terms of solid content, ofa slurry of a rubber reinforcing carbon black having amorphous silicadeposited on the surface thereof.
 3. A rubber composition as claimed inclaim 2, wherein the rubber reinforcing carbon black prior to thedeposition of the amorphous silica is a GPF to SAF grade produced by theoil furnace method.
 4. A rubber composition as claimed in claim 2 or 3,further comprising 5 to 150 parts by weight of an aromatic process oiland/or high viscosity oil.
 5. A rubber composition as claimed in any oneof claims 2 to 4, wherein the content of the amorphous silica is 0.1 to20% by weight of the surface-treated carbon black.
 6. A rubbercomposition as claimed in claim 1 which is a rubber composition for tireuse comprising at least one rubber containing a diene rubber to which isblended surface-treated carbon black composed of rubber reinforcingcarbon black having a nitrogen specific surface area (N₂ SA) of 25 to250 m² /g and a DBP oil absorption of 70 to 180 ml/100 g on the surfaceof which is deposited 0.1 to 20% by weight of silica.
 7. A rubbercomposition as claimed in claim 6, which is for tire cap or under treaduse, wherein the carbon black prior to the surface treatment has anitrogen specific surface area (N₂ SA) of 55 to 250 m² /g and a DBP oilabsorption of 70 to 180 ml/100 g, and the amount of formulation of thesurface-treated carbon black is 10 to 200 parts by weight based upon 100parts by weight of the rubber.
 8. A rubber composition as claimed inclaim 7, which is for tire side tread use, wherein the carbon blackprior to the surface treatment has a nitrogen specific surface area (N₂SA) of 25 to 120 m² /g and a DBP oil absorption of 70 to 150 ml/100 g,and the amount of formulation of the surface-treated carbon black is 10to 100 parts by weight based upon 100 parts by weight of the rubber. 9.A rubber composition as claimed in claim 6, which is for covering tirebelt cords, wherein the carbon black prior to the surface treatment hasa nitrogen specific surface area (N₂ SA) of 70 to 150 m² /g and a DBPoil absorption of 70 to 150 ml/100 g, and the amount of formulation ofthe surface-treated carbon black is 10 to 100 parts by weight based upon100 parts by weight of the rubber.